The invention relates to a device and method for sampling the first flush of runoff water from a storm or simply sampling any liquid discharge where a pure sample of the discharge is required.
The first flush of storm water runoff is typically the most chemically contaminated and poses the greatest environmental risk as compared to subsequent flows. Accordingly, the need is becoming more apparent by association with the problem or by government regulation to obtain the first flush of storm water runoff so that chemical and toxicological characteristics can be made for monitoring and risk assessment purposes. Many samples may be necessary to characterize the flows contributing to a discharge stream to assess multiple discharge sites.
Measuring runoff is more difficult than measuring point source discharges due to episodic flows and flow-variant chemical concentration. Currently, equipment primarily designed for continuous point source discharges have been adapted for use in nonpoint source monitoring. Typical commercial samplers used to measure runoff are microprocessor controlled to draw a sample through an intake tube inserted in the discharge stream. The problems are numerous. The surface film is not included in the sample. For near source sampling, slow solubility kinetics result in a discharge stream that is not chemically homogeneous, and especially in the case of hydrophobic chemicals, such as nonpolar organics, most of the contaminant mass can occur as a surface film. Under very contaminated conditions, the water may not be able to dissolve the contaminant loads so that even at far downstream sites mid water column samples are biased in their representation of the true contaminant flux. Many sites must be sampled. Of course, large numbers of commercial water samplers or large work crews with "jars in hand" could be employed. Obviously, this is cost prohibitive and there is a need for a low cost and easy to use sampler for obtaining a true sample of the first pulse of storm water runoff.